Oak leaf from the first oak wilt detection site in Sheboygan County, showing bronzing coloration characteristic of oak wilt infection. Photo: William McKnee, WI DNR

Oak wilt, a deadly fungal disease affecting the red oak group, was recently detected in Sheboygan County for the first time. Wood samples were collected from adjacent symptomatic oak trees on the Kettle Moraine State Forest – Northern Unit in the Town of Mitchell after the trees were spotted by DNR Forestry staff. The presence of Ceratocystis fagacearum, the fungus causing oak wilt, was confirmed through a DNA test done at the DNR Forest Health Lab and DNA sequencing done at the UW-Madison Biotechnology Center. On-the-ground control options are currently being examined.

Oak wilt is a common disease in the southern two-thirds of the state, but has been

Map of counties where oak wilt has been detected, with the recent Sheboygan County confirmation shown in orange.

increasingly found in the northern counties. DNR staff have recently reported first community detections in these northern counties already known to have the disease: